Japan's Tokyo Electric Power Co (Tepco) has started the fourth discharge of ALPS-treated water to the sea from the damaged Fukushima Daiichi NPP. In line with the previous three discharges, the release will include 7,800 cubic metres of water over some 17 days after tests confirm that the radioactivity level meets the standards set by the government and the utility. This will be the last discharge for the fiscal year ending March. No abnormal tritium levels were detected in nearby waters following the previous three discharges, according to Tepco.

The tritium concentration in the third batch of diluted water treated with the Advanced Liquid Processing System (ALPS) released in November was far below Japan’s operational limit, International Atomic Energy Agency (IAEA) experts present at the site confirmed.

The water was accumulated after the NPP was crippled by the massive earthquake and tsunami that struck northeastern Japan in 2011 resulting in the core meltdown of three reactors. Water was used to cool the reactors. In total, 1.34m tonnes of radioactive wastewater is stored in about 1,000 tanks at the plant, which are almost full and need to be emptied to enable decommissioning of the plant to proceed.

The processed water is diluted with seawater to one-fortieth of the concentration permitted under Japanese safety standards before being released one kilometre off the power plant via an underwater tunnel.

Tepco said that, for subsequent discharges, it will omit the step of temporarily storing the treated water in a large tank to check the tritium level before release. Instead, it will check the level as the water flows through pipes as it did in the past three rounds. The company is expected to release treated water over some 30 years.

China continues to oppose the water release and has banned Japanese seafood imports since the first discharge in late August. Chinese Foreign Ministry spokeswoman Mao Ning said Beijing "firmly opposes" the ocean discharge and requests Tokyo to "stop this wrongdoing”.

Meanwhile, Japan's Ministry of Foreign Affairs has said International Atomic Energy Agency Director General Rafael Mariano Grossi pay a visit to Japan on 12-14 March during which he will visit Fukushima Prefecture. The visit "is expected to contribute to the further strengthening of the relationship between Japan and the IAEA in a wide range of areas, including the response to the discharge of ALPS treated water into the sea", the Ministry noted.

Image: Fukushima nuclear power plant in Fukushima prefecture, Japan